From fbddfd24cf85b632794e02f57ad716d300f16312 Mon Sep 17 00:00:00 2001
From: Ibrahim Jarif <ibrahim@dgraph.io>
Date: Fri, 13 Mar 2020 21:05:29 +0530
Subject: [PATCH] Add BypassDirLock option (#1243)

Fixes https://github.com/dgraph-io/badger/issues/988
Based on https://github.com/dgraph-io/badger/pull/1046

This PR adds `BypassDirLock` option which allows badger to work without
acquiring a lock on the data directory. This option could lead to data
corruption if used with multiple badger instances trying to write to
the same badger directory.

Co-authored-by: Ehsan Noureddin Moosa <ehsannm@users.noreply.github.com>
(cherry picked from commit 1bcbefc03c753b0ad91a8cdf350532b42b47fb5a)
---
 db.go      | 44 +++++++++++++++++++++++---------------------
 options.go | 18 ++++++++++++++++++
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/db.go b/db.go
index f7d8473e5..05a8a276c 100644
--- a/db.go
+++ b/db.go
@@ -234,33 +234,35 @@ func Open(opt Options) (db *DB, err error) {
 		if err := createDirs(opt); err != nil {
 			return nil, err
 		}
-		dirLockGuard, err = acquireDirectoryLock(opt.Dir, lockFile, opt.ReadOnly)
-		if err != nil {
-			return nil, err
-		}
-		defer func() {
-			if dirLockGuard != nil {
-				_ = dirLockGuard.release()
-			}
-		}()
-		absDir, err := filepath.Abs(opt.Dir)
-		if err != nil {
-			return nil, err
-		}
-		absValueDir, err := filepath.Abs(opt.ValueDir)
-		if err != nil {
-			return nil, err
-		}
-		if absValueDir != absDir {
-			valueDirLockGuard, err = acquireDirectoryLock(opt.ValueDir, lockFile, opt.ReadOnly)
+		if !opt.BypassLockGuard {
+			dirLockGuard, err = acquireDirectoryLock(opt.Dir, lockFile, opt.ReadOnly)
 			if err != nil {
 				return nil, err
 			}
 			defer func() {
-				if valueDirLockGuard != nil {
-					_ = valueDirLockGuard.release()
+				if dirLockGuard != nil {
+					_ = dirLockGuard.release()
 				}
 			}()
+			absDir, err := filepath.Abs(opt.Dir)
+			if err != nil {
+				return nil, err
+			}
+			absValueDir, err := filepath.Abs(opt.ValueDir)
+			if err != nil {
+				return nil, err
+			}
+			if absValueDir != absDir {
+				valueDirLockGuard, err = acquireDirectoryLock(opt.ValueDir, lockFile, opt.ReadOnly)
+				if err != nil {
+					return nil, err
+				}
+				defer func() {
+					if valueDirLockGuard != nil {
+						_ = valueDirLockGuard.release()
+					}
+				}()
+			}
 		}
 	}
 
diff --git a/options.go b/options.go
index 0e3c60e3f..f11ce3f8c 100644
--- a/options.go
+++ b/options.go
@@ -84,6 +84,11 @@ type Options struct {
 	EncryptionKey                 []byte        // encryption key
 	EncryptionKeyRotationDuration time.Duration // key rotation duration
 
+	// BypassLockGaurd will bypass the lock guard on badger. Bypassing lock
+	// guard can cause data corruption if multiple badger instances are using
+	// the same directory. Use this options with caution.
+	BypassLockGuard bool
+
 	// ChecksumVerificationMode decides when db should verify checksums for SSTable blocks.
 	ChecksumVerificationMode options.ChecksumVerificationMode
 
@@ -575,3 +580,16 @@ func (opt Options) WithZSTDCompressionLevel(cLevel int) Options {
 	opt.ZSTDCompressionLevel = cLevel
 	return opt
 }
+
+// WithBypassLockGuard returns a new Options value with BypassLockGuard
+// set to the given value.
+//
+// When BypassLockGuard option is set, badger will not acquire a lock on the
+// directory. This could lead to data corruption if multiple badger instances
+// write to the same data directory. Use this option with caution.
+//
+// The default value of BypassLockGuard is false.
+func (opt Options) WithBypassLockGuard(b bool) Options {
+	opt.BypassLockGuard = b
+	return opt
+}